Receiving system



w. A. MacDoN-A'LD l Feb. 28, 1928.

BECEVING SYSTEM Filed Oct. 8, 1925 3 Sheets-Sheet 1 @s ik.

lNvENToR lll W////0m Macono/d ATTORNEYS 'El-JM Feb. 2s, 192s.

W. A. MaCDONALD RECEIVING sYsTM Filed het. s, 1925 3 sheets-sheet 2 ATTORNEYS w. A. MacDo'NALD RECEIVING sys-TEM Feb. 428,v 1928.

Filed O61'. 8, 1925 in m MTORNEYQ Patented Feb. 28, 1928.

Um'ri-:Dv 4STATES WILLIAM A. MACDONALD, F LITTLE NECKQNEW YORK, ASSIGNOR T0 HAZELTDUI CORPORATION, 0F JERSEY CITY, NEW JERSEY, A CORPORATION 0F DELAWARE.

RECEIVING SYSTEM.

application and 0mm s, 1925. serial No. claas.

This invention relates to methods and arrangements for utilizing the harmonicfrequencies appearing in the output clrcuit of a detector or recti er of a radio recelver for increasing the amplification of received signals and for increasing the selectivity of the receiver.l n

'It is well known that a rectified alternating current contains a certain ortion of l0 the fundamental frequency whic has escaped rectification, together with various harmonic frequencies of the fundamental,

Ythe amplitude of the series of harmonics decreasing in proportion as the harmonic l5 series progresses.

.In modern radio reception, rectification or detection of some form is required to render the incoming `radio-frequency signal waves audible. It was customary in past practice to utilize only the audio-frequency component developed from the rectified portion of the incoming or fundamental radio frequency, and to short-circuit, remove' or neglect the harmonics or higher multipleradio frequencies appearing 1n the output circuit of the detector. A single exceptlon to this.I practice occurs wherein the fundamental radio-frequency energy appearing in the output circuit of the detector Yis returned 3" to the input circuit thereof and vrredetected. This action isknown as regeneration, and is the subject-matter of Armstrong U. S. Patent No. 1,113,149. f

In the present arrangement, it is proposed v:l5 to utilize the harmonic radio frequencies with the objectl of amplifying them to a desiredV value, rectifying them and then employing them directly or in conjunction with other rectified high frequencies, to increase 4U the amplification, in audible form, of the received signals.

It, has been recognized that there is a certain limit to the amplification which it is possible to obtain in a multistage radio-frequency amplifier, because of the difficulty in' controlling oscillations which not only render the radio receiver unstable, but tend to generate influences which mask the desired signals. By utilization of the present -f* invention it is possible to realize-the maxi-` mum amplification possible at the 'fundamental radio frequency, and then, by pro erly arranging the output circuit o t e detector 0r rectifying means, such as a 65 vacuumtube, to utilize the first harmonic ,amplified as much as is practicab or double frequency of the fundamental. This harmonic frequency is then referably lie without producing disturbing oscillations. The amplified first harmonic frequency, when rectified, can be combined with the audiofrequency component of the fundamental to give increased si nal strength. It is thus possible by amp if 'n individual si als of diffef'ent harmonic1 equencies, to o tain greatly increased amplification without pro-- vducing undesirable oscillations.

rther advantage of the invention is that of greatly increased selectivity. It will readily be understood that signals of a frequency other thanthe fundamental, no matter how strong they may be, cannot force themselves through the series of tuned amplifiers, because each successive amplifier is tuned to a frequency which differs widely from the others. In other words, the only radio energy which can interfere `withthe signals received upon apparatus arranged rradio frequency thereof is disregarded, andV in which only the double frequency of the first harmonic is utilized to obtain an audible signal;

Fig. 2 represents a schematic showing of a modification of the present invention :in

which the audio-frequency components of the fundamental radlo frequency, the first harmonic thereof, and the first harmonic of the latter are combined and introduced into theinput circuit ofan audio-frequency amplifier; l,

Fig. 3- is a third modification of the invention in `which the first and second harino monies appearing in the output circuit of the I lfirst detector are'amplified and rectified, and

thereafter combined with the audio-frequency component of the fundamental frequency, and subsequentl introduced into the input circuitof an-'au io-frequency amplifier; and v' Fig. 4 represents one form of a diagraml Y matic circult arrangement incorporating the present invention in a radio receiver, from which it will be possible to understand more cle'arly the circuits suitable for radio-frequency amplification and detection in the 'schematic illustrationsshown in Figs. 1, 2 and 3.

Referring especially to Fig. 1, indicates an antenna, which may be of any Well- A quency of the incoming signal, altho'ugh this invention is not limited to such tuned circuits. The output circuit Aof the radio-fre- .quency amplifier 6 is coupled by means of a trans ormer 7 to the input circuit of the usual detector or rectifier 8, which is preferably of the vacuum tube type. As is Well known, such a detector, or rectifier, serves to rectify the radio-frequency signals amplified by amplifier 6, so that the rectified si als are rendered capable of operating sultable audio-frequency amplifying appa-" ratus. It is also well known that, due to the rectifying action of the detector, there are mental radio present inthe output circuit thereof the which occur in the simple harmonic series.

In the output circuit of the first detector 8, therefore, appears the rectified or audiofrequ'ency component -of the fundamental radio frequency,'and also the first, second,

third and higher harmonics of that funda.

mental frequency.v It will be understood that the first harmonic is usually the strongest of the series, and that the succeeding harmonics progressively decrease in amplitude throughout the series. lIn the arrangev ment of Fig. 1, under consideration, the audio-frequenc component of the fundafiequency is disregarded, but the rst harmonic radiol frequency is introduced into the input circuit of an amplifier 9 by means of a transformer 10. Amplifier 9 may consist of one or more tuned stages, each stage including at least one vacuum tube for the purpose ofl amplif ing the first harmonic radio frequency. i he output circuit of the last stage of amplifier 9 is coupled, by means of a transformer 11, to the input circuit of a second detector 12, while the transformer 13 serves to introduce an harmonic radio frequency, double that amplified by the second amplifier 9, into the input circult of a third amplifier 14, the output circuit of which is coupled to a thirddetector 15 by' means of transformer 16. The output circuit of this detector includes an audio-frearmonic frequencies of the fundamental 26 which .serves Aquency indicating device such as a telephone,

net result of this arrangement is that the indicating device T is operated only by the audio-frequency component of a frequency corresponding to )the fourth harmonic of the fundamental radio frequency, i. e., thefirst .harmonic of the first harmonic of the fundamental frequency. Such an arran ement provldes an extremely hlgh degree o selecpass the series of harmonic filter systems unless thosesignals be of a frequency identical with the fundamental radiofrequency. The degree of amplification finall' attainable is also greater than could be obtained by a straight multistage radio-frequency amplifier, because each amplifier, namely, 6, 9 and 14, may include within itself as' many component amplification stages as are practicable at the frequency to which that amplifier is tuned.

Referring to Fig. 2, there is indicated an antenna 56 coupled by means of a transformer 57 to the input circuit of a radio-frequency amplifier 17. This-amplifier, which may include one or more tuned or untuned stages of vacuum tube amplification., amplifies the fundamental radio-frequency signals intercepted by antenna 56. The output sol ltivity, because interfering signals' cannot circ-uit of amplifier 17 is coupled by means of quency into the input circuit of amplifier 22.

This amplifier may include one or more amplifying stages, each having one or more vacuum tubes and the customary associated circuits. The output circuit of amplifier 22 is coupled by means of transformer -23 to the input-circuit of a second4 detector 24, and the output circuit of this last-mentioned detector includes the second primary winding 25 of audlo-frequency .transformer 58, and also includes the primary winding of a transformer of the second detector to the in ut circuit of a third radio-fre uency vampli er 27. Amplifier 27 may inc nde one or more tuned or untuned stages of amplification each having to couple the output circuit neeopso one or more vacuum tubes. Transformer 26 introduces "the first harmonic of the frequency rectified by detiector 24 into the input circuit of amplifier 27, while the output circuit of this last amplifier is coupled by means of a transformer 28 to the input circuit of a third detector 29, vthe output cir-v cuit of which includes a third primary winding 30 of the mentioned audio-frequency transformer 58. The windings 20, 25 and 30 in the output circuits of detectors 19, 24r

and 29, respectively, couple these circuits through transformer 58 to the input circuit of an audiofrequency amplifier 31. This amplifier may consist of one or more vacuum tubes arranged in circuits now well known, and includes an output circuit for controlling a telephone, or loud s eaker, T.

It will be ,seen that in this last-considered arrangement, the received signal is amplified and then rectified, after which `the first harmonic frequency a pearing in the output circuit of the first et'ector is amplified and rectified; thereafter the first harmonic frequency appearing in the output circuit of the second v whereupon the three rectified audio-fre- (iuency components are combined in a transormer, then amplified and caused to actuate a telephone, or other indicating device.

At' this point it should be noted that each radio-frequency amplifier, regardless of the number of stages therein, may be considered, to fo lowing,as a unit or group, which is preferably operated on a single -frequenc I. For' instance, in Fig. 1,'components 5, 6, and 8 operate on the fundamental; 9, 11v and 12 operate on the rst harmonic; and 13, 14, 16 and 15 operateon the first harmonic of the first harmonic, or double the fr uency of the first harmonic of the fun amental. Likewise, ieferring to Fig. 2,1components 56, 17, 18 and 19 operate on the fundamenl tal; 21, 22, 23 and 24 operate on the first harmonic; and 26,27, 28 and 29 operate on double the frequency of the first harmonic of the fundamental.' The components, or apparatus, of Figs. 3 and 4 may be similarly grouped.

Fig. 3 shows a slightl modified arrangiement of that shownin ig. 2, and indicates anv antenna 32, which is coupled by means of ythe first harmonic of radio-f uency transformer 33 to the input circuito an amplifier 34. This amplifier may be ofthe type previously mentioned, consisting of several stages of tuned or untuned radio-frequency amplification, each of which includes a vacuum tube.. The output circuit of this amplifier is coupled by means of a transformer 35 to the in ut circuit of a detector 36, the out ut circuit of which includes primary win ings of the transformers 37, 39 and 42. Transformer 37' introduces the fundamental radio etector is amplified and rectified,

ether with the rectifier or detector next' frequencyV intovamplifier 38, which may consist of one or more stages arranged for 4vacuum ytube am lification. The output cirwinding 61 of audio-frequency transformer 39. Transformer 42 introduces the second harmonic of the fundamental radio freuency into am ilifier v43, which may be of the character o amplifier 38, and amplifier 43 is in turn coupled to a third detector 44 by means of transformer 45. The output circuit of this detector includes the primary winding 46 of audio-'frequency transformer 39, which introduces the combined fre uenc'iesdeveloped in the out ut circuitso the three detectors, 36, 41 an 44, into the input circuit of audio amplifier 47, which may be of the multistage vacuum tube type and whose output circuit includes' a telephone, or other indicating device, 48.

The arrangement shown in Fic. 3, it will be observed, differsfrom that of Fig. 2 in that the second harmonic of the fundamental frequencyis utilized as well as the first harmonic.

hisis made possible becauseof the` and 42 are connected in series with the out put circuit ofthe first detector, in which circuit both the first and second harmonics of thefundamental freiuency 4are y present. Of

course the third an higher harmonics ai'e present as well, but in this example onlytlie rst and second` have been utilized. The first harmonic is amplified by amplifier 38, and the second, harmonic byamplifier 43. The fundamental and the first and second harmonics are rectified by detectors 36, 41

and 44, respectively, after which the audiofrequency signals are combined in transformer 39, amplified at 47,' and indicated at 48.

The figures herewithillustrate the'lcou-l pling means betweenv the amplifiers and detectors as being 'of the electromagnetic' type. This showing of couling transformers, such as 7, 16, 57., 23, 26, 2 and Tm is for convenience only, since other coupling means, as, for instance, capacitive, or resistive, might be' used with equal success.

Referring to'Fig. 4, there is' indicated an antenna directly connected to the inputfcircuit of vacuum' tube V1, which is tuned by inductance T, and variable condenser C1. The plate circuit'of vacuum tube V1 is vconnected by means of radio-frequency transformer T2 to the input circuit. of vacuum tube V2. This last-mentioned input circuit is tuned by means of variable condenser C2 connected across the secondary ,of transformer T2. In accordance with well-known practice, a neutralizing condenser Cm, connected to the grid of vacuum tube V1 and to oan appropriate point on the `secondary wind;

ing of transformer T2, functions to neutral-- ize undesirable capacitlve coupllngbetween the input circuit and the output c n'cultfof -vacuum' tube V1. The output circuit of vacuum tube V2 is coupled by means of radio-frequency transformer T3 to the input circuit of detector Vm which lincludes varicuit of vacuum tube V2. Vacuum tubes Vl and V2, together with associated input and output circuits as described, constitute a tuned radio-frequency amplifier, which is suitable for use 1n the previously described arrangements. Any number of similar stages may be employed within practicable limits.

The output circuit of detector V3 includes' primary winding '50' of the audio-frequency transformer 51, and also the prima-ry winding 52 of transformer T4. A by-pass condenser 53 is connected across the primary winding 50, and avariable 'tuning condenser C4 is lconnected across theprimary 52 of transformer T4. The secondary winding of transformerll.. isshunt'ed b variablecon-Jngfrom the s irit r, t Y

il rdenser C5 to tune the input circuit of the Aamplifying tube V5,

second detector V4, th'e output circuit of which includes a second primary windingv 54 of audio-frequency transforme-r 51. Thls means OI lmpI'GSSlng an lncomlng signal last-mentioned winding is shunted by a bypass condenser 55. Primary windingsl 50 and 54, included in the output circuits of the respective detectors V3 and V4, serve to 4 might be employed in accordance with this invention with .more or less satisfactory results, depending upon the circumstances. For instance, in the lace vof any of the 'radio-frequency amplifiers, K

of Fig. 1, or 38,01* 43 of Fig. 3, a radio-frequency amplifier of the super-heterodyne type might well be used. Again, increased amplification might be obtained if one or more of the amplifiers were of the wellknown resistance coupled type, followed by a. detector tuned tothe second harmonic of' the current which is being amplified, rather than to the same frequency as suggested in the other examples herein. If such a system were used in the circuit `of Fig. 1, amplifier 6 might be tuned to the fundamental, detector 8 to the second harmonic thereof, amplifier9to the first harmonic of the frequency ofthe currentin detector 8, which would be six times the 'frequency of the fundamental, and so on.

It -will be understood that the present disclosure is merely typical of applicants invention, and that there may he innumerable variations in the types of amplifiers, in thecombinations of the detectors and amplifiers, inthe harmonic frequencies utilized, and in the methods of combination of the audiofrequ'ency components, tall within the scope of the appended claims and without depart! of this invention.

I W 1. In a radio receiving `systemiincluding a plurality of amplifiers and detectors,

uponl a first amplifier responsive to the frequency of said signal, a first detector linked with said first amplifier andA responsive to the frequency of said signal, an output cirsuch as 6 or 14A couple those detectors to the audio-frequency cuit for said detector in which occur a plu- Y.

amplifier, the vacuum tube of which is designated V5. The rectified signals appearing in the output circuits of the detectors are amplified by the audio-frequency amplifier, which in turn actuates a telephone, or loud speaker, LS.

In operating the receiver illustrated in Fig. 4, the input circuits of vacuum'tubes V1, V2 and V3 would normally be tuned to the incoming, or fundamental, radio frequency. Accordingly, transformer T4 would be tuned to the first harmonic of the fundamental frequency. The detector V, would then rectify this first harmonic frequency, and combine, in audio-frequency transformer 51, the audio component thereof with the audiov component of the fundamental frequency derived from detector V3. The audio-frequency currents from the two detectors would then be amplified byaudioand .actuate loud speaker L A v Radio-frequency amplifiers of types other ated..

ralitly]7 of-frequencies which are harmonics of t e frequency of said incoming signal, means for separately amplifying and detecting said harmonic frequencies, and means' for combining'the audio-frequency currents in the output circuits of saidv detectors whereby an indicating device may be actu- 65 than that described in connection with Fig. quency, amplifying and rectifyingv said lll source of modulated incoming high-frequency waves, a detector operative to rectify said Waves and .to produce therefrom an audio-fret uency current in accordance with the moduiation of the waves and, `in addil tion, an harmonic of the incoming wave,

a second detector adapted to rectif said harmonicwave and to produce there rom a second audio-frequency current, 'signal-indicating means, and means for additively combining said alulio-frequencyv currents and impressing the combined currents' upon said signal-indicating means.

5. In a wave signal receiving system a' receiving detector, an 'amplifier fomamplifying received waives, a vacuum tube detector` for rectifyingl the amplified received waves, said detector having an output circuit in which are-present both the audio-frequency component of the rectified waves and one o1' more harmonic-freqllencycomponents of the received Wave, a second vacuum tube detectorhavin an input .circuit tunedto the -frequency o. one `of said harmonics and coupled to the output circuit of said first detector, said second detector being operative to rectify waves of the harmonic frequency to which its input circuit is tuned and to produce thereby7 audio-frequency eurrents corresponding in form to those produced in the output circuit of said first detector, an audio transformer connected to the output circuits of said first .detector and said second detector conjointly, said trans-` former vbein operative to additively combinesaid au io-frequency currents, and signal-indicating means' ada ted to be operated by said combined audiorequency currents.

6. In a` wave si. aling system, a source of incoming highrequency waves'of a fundamental frequency, means operative to rectify said, waves and to produce there.- from current of an effective frequency considerably less than that of said fundamental n frequency and also to produce an harmonic fundamental frequency, fa second of said yan amplifier for amplifyin -means operative to' rectif said harmonic frequency and to produce t erefrom current of a frequency. considerably less than that of said harmomc frequency, and means for combining said currents, whereby signalindicating means may be operated b the current resulting from said combine currents. i

7. In a' Wave signal receiving system a source of modulated incoming radiorequency Waves, a first rectifierzhavingan output clrcuit and operative to rectify in part said radio-frequency Waves to produce therefrom an'andio-frequency current in accordance with the modulation of the Waves, and also to produce an harmonic of'said radiofrequency waves, a second rectifier linked to the output circuit of said first rectifier and operative to rectify a certainradio-frequency current occurring in the output circuit of. said first rectifier and to produce therefrom a second audiorequency current, a third rectifier linked Ato the output circuit of said first rectifier and operative to' rectify a certain harmonic of the incoming radiofrequency current and to produce therefrom va third audio-frequency current, and means for additively combining said audio-frequency currents, and impressing the. resulty ing current upon a signal-indicating means.

8. In a Awave signal receiving system a' source of vmodulated incoming radiorequency waves of a fundamental frequency, the. received Waves, a detector for rectifymg said waves whereby a plurality of harmonics of said.

fundamental frequency and an audio-frequency component thereof are produced, al second detector linked to said first detector for rectifying one of said harmonics whereby a second audio-frequency component is produced, a third detector linked to said first detector for rectif inv anotherof said harmonics, whereby a t iird audio-frequency component produced, and means for additively combinlng said audio-frequency-components and impressing the resulting current upon a signal-indieatinv means.

In testimony whereof I afix my signature.

WILLIAM A. MACDONALD. 

